On August 7th, SM Entertainment has announced that f(x) will be continuing on as a four-member group, without Sulli, after much speculation. Entertainment released a statement to fans and media revealing that Sulli will no longer be joining f(x) in their promotions, much to fans’ dismay.
The statement reads, “[We] negotiated with Sulli and decided to respect her wishes to leave f(x) and focus on her acting. She is currently on break and will be working on her future activities.”
This news comes after rumors of Sulli leaving and being spotted on multiple dates with her boyfriend, Choiza. According to SM Entertainment on August 7th, “We have discussed her future activities with Sulli who is currently taking a break with minimal activities. We have decided to respect her wishes and she will be officially leaving f(x) and focusing on her acting career. Following this f(x) will be going ahead as a four-member group with Victoria, Luna, Amber, and Krystal. f(x) is receiving much love for their unique music and each of them is becoming well-respected artists in their own rights. We plan to support f(x) and Sulli fully in their activities.”
source: koreaboo
Wow, I was kind of hoping she would stay but I understand her reasons for leaving.

Wanted sulli to stay. She's the reason I got into f(x). Honestly this makes me dislike SM and korean "netzins" more. If they protected the love artist then members wouldn't leave. So Shinee is the only SM long time group that hasn't lost a member yet. 😣😣😣😦😦